The design for a simple portable computer that only requires a pen and a piece of paper.

The computer consists of a sheet of paper that contains both the program as well as a number of data registers, that will be used to represent the contents of the registers.

To begin, the pen, representing the program counter, is positioned at the line 00 of a program. The instruction in that line is then processed by the user by either moving the pen(program counter), modifying the value of a data register or by checking if a data register has become zeroed.

Primitives

Most models contain a few arithmetic operations and at least one conditional operation. Three base models, each using three instructions, are drawn from the following collection. In addition, a machine usually has a HALT instruction, which stops the machine.

• CLR(r): CLeaR register r. (Set r to zero.)
• INC(r): INCrement the contents of register r.
• DEC(r): DECrement the contents of register r.
• CPY(rj, rk): CoPY the contents of register rj to register rk leaving the contents of rj intact.
• JZ(r, z): IF register r contains Zero THEN Jump to instruction z ELSE continue in sequence.
• JE(rj, rk, z): IF the contents of register rj Equals the contents of register rk THEN Jump to instruction z ELSE continue in sequence.

The following three counter machine models have the same computational power since the instructions of one model can be derived from those of another:

• INC(r), DEC(r), JZ(r, z) — Minsky (1961, 1967), Lambek (1961)
• CLR(r), INC(r), JE(rj, rk, z) — Ershov (1958), Peter (1958)
• INC(r), CPY(rj, rk), JE(rj, rk, z) — Elgot-Robinson (1964), Minsky (1967)

WDR Instruction Set

The WDR paper computer or Know-how Computer is an educational model of a computer consisting only of a pen, a sheet of paper, and individual matches in the most simple case. The instruction set of five commands is small but Turing complete and therefore enough to represent all mathematical functions: incrementing ("inc") or decrementing ("dec") a register, unconditional jump ("jmp"), conditional jump ("skp", skips next instruction if a register is zero), and stopping program execution ("end").

Punched card

To encode a WDR program into a 8-bits punched card, we could use 3 bits of space to encode the operation, which leaves 5 bits for the value. This computer's programs uses only 5 operations out of a possible 8, leaving 3 unused.

The following program subtracts from R1 and adds to R0 until the value of R1 is zero. The result of the addition of R0 and R1 will be stored in R0.

The binary expression of the operation and value of the previous program can be encoded horizontally as the following punched card:

	v   v   v   v   v   v    
			•                
	•   •           •        
		•       •            
							 
							 
							 
	•                        
	•       •   •   •        

Ref. 5-bits Table

The following table show the binary table for 32 addressable lines of a program.

CARDIAC Instruction Set

CARDIAC (CARDboard Illustrative Aid to Computation) is a learning aid developed for Bell Telephone Laboratories in 1968 to teach high school students how computers work. The computer operates in base 10 and has 100 memory cells which can hold signed numbers from 0 to 999. It has an instruction set of 10 instructions which allows CARDIAC to add, subtract, test, shift, input, output and jump.

• WDR Paper Computer
• CARDIAC Paper Computer
• Human-Computers
• Rustic Computing

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